ID Needed

Finally after about a year of being stable, I now have large amounts of Amphipods and/or copipods. Great stuff, no fish currently to keep it under control but it's fine and not a problem yet.

A few weeks ago, finally, I have finally started getting some rather nice purple coraline on my LR - yay! It's about time.

A week or two ago, I started noticing a semi large amount of these guys...

All over my LR (not THAT many), but strangely, hundreds of them in my sump. They look almost like a very small version (5mm or so) version of those shells that 'stick' to the rocks in the ocean that hurts your feet so badly.

The amounts in the DT are not that high (from what I can see), maybe 10 or 15 currently. Sump literally has hundreds of them stuck against the glass though.

What are they? Friend / Fo? Do I need to stress about them? They look harmless, I haven't really noticed anything that they are doing that seems to be harmful - but granted, I have a sneaky suspecion that these guys are still very small.